As advanced nuclear reactor designs move forward in commercial development, many of them will use TRISO particle fuel, a highly robust uranium fuel that can withstand extreme temperatures without melting. TRISO fuel includes pyrolytic carbon, which is a graphene-based material with a disordered atomic structure.
When subjected to harsh mechanical stresses and irradiation in an advanced reactor, the fuel material’s microstructure will change or evolve, often causing undesirable changes in the overall properties and degrading the fuel’s performance.
Raphaëlle David
“It’s important to understand the extent of those changes in the material because that will determine how long the fuel can be used,” says Raphaëlle David, a PhD student in nuclear engineering and engineering physics at UW-Madison. “For instance, if the material’s properties change dramatically within two months, that fuel won’t work well for a nuclear reactor.”
However, it has been challenging to sufficiently characterize how pyrolytic carbon evolves over time in extreme conditions. “There has been a huge gap in the tools that we need to describe the material’s evolution,” David says.
To address this problem, David and NEEP Associate Professor Yongfeng Zhang have developed new computational tools that provide a much better description of the complicated microstructure of pyrolytic carbon materials across multiple length scales. These tools will allow researchers to understand how the material changes over time.
David and Zhang detailed their results in a paper published in the journal Carbon in May 2025.
“I really enjoy studying things at very small scales with computational models because it leads to fundamental knowledge than can have wide-ranging applications,” David says. “For example, our framework and new tools can also enable improved characterization and analysis of a broad class of carbon materials derived from graphene—materials that are used extensively for many applications in diverse areas and industries beyond nuclear power.”
This work was supported by the U.S. Department of Energy’s Nuclear Energy University Program (Grant No. DE-NE0008979 and DE-NE0009456).
Featured image caption: TRISO particles can also be fabricated into billiard ball-sized spheres called “pebbles” for use in either high-temperature gas or molten salt-cooled reactors. Credit: DOE.